A team of food scientists has developed a sensor that can detect the potentially deadly bacteria Listeria monocytogenes in less than 24 hr at concentrations as low as 1,000 cells/ml of fluid. This amount of fluid is about the size of a pencil eraser. The sensor also is selective enough to recognize only the species monocytogenes.

Known as an "optical biosensor," the device uses light to detect the presence of a target organism or molecule. The sensor is made of a small piece of optical fiber that is coated with an antibody that specifically recognizes L. monocytogenes, captures it, and binds it to the fiber. When the fiber is placed in a liquid food solution, any L. monocytogenes in the sample will stick to the fiber.

The selectivity, sensitivity and rapidity of this sensor represent a vast improvement over the types of test kits that are currently available commercially, say scientists at Purdue. Collectively, these qualities make this research an important contribution in the field of food safety.

The sensor also is selective enough to recognize cells of L. monocytogenes when other types of foodborne contaminants, such as salmonella or E. coli, are present.

Listeriosis, the illness caused by consuming Listeria-contaminated foods like deli meats or cheese, leads to higher rates of hospitalization and mortality than any other foodborne illness. The mortality rate for people with listeriosis is high, and for this reason, the FDA has a zero-tolerance rule for Listeria. There should be none at all in any ready-to-eat products.

According to the Centers for Disease Control and Prevention, approximately 2,500 people develop listeriosis annually, and approximately one in every five cases is fatal. The elderly, pregnant women, newborn infants and individuals with compromised immune systems are most at risk of contracting the disease.